<!DOCTYPE HTML>
<html>

<head>
  <meta charset="utf-8">
  <title>菜鸟教程(runoob.com)</title>
  <style>
    .error {
      color: #FF0000;
    }
  </style>
</head>

<body>

  <?php
  // 定义变量并默认设置为空值
  $nameErr = $emailErr = $genderErr = $websiteErr = "";
  $name = $email = $gender = $comment = $website = "";

  if ($_SERVER["REQUEST_METHOD"] == "POST") {
    if (empty($_POST["name"])) {
      $nameErr = "名字是必需的";
    } else {
      $name = test_input($_POST["name"]);
      // 检测名字是否只包含字母跟空格
      if (!preg_match("/^[a-zA-Z ]*$/", $name)) {
        $nameErr = "只允许字母和空格";
      }
    }

    if (empty($_POST["email"])) {
      $emailErr = "邮箱是必需的";
    } else {
      $email = test_input($_POST["email"]);
      // 检测邮箱是否合法
      if (!preg_match("/([\w\-]+\@[\w\-]+\.[\w\-]+)/", $email)) {
        $emailErr = "非法邮箱格式";
      }
    }

    if (empty($_POST["website"])) {
      $website = "";
    } else {
      $website = test_input($_POST["website"]);
      // 检测 URL 地址是否合法
      if (!preg_match("/\b(?:(?:https?|ftp):\/\/|www\.)[-a-z0-9+&@#\/%?=~_|!:,.;]*[-a-z0-9+&@#\/%=~_|]/i", $website)) {
        $websiteErr = "非法的 URL 的地址";
      }
    }

    if (empty($_POST["comment"])) {
      $comment = "";
    } else {
      $comment = test_input($_POST["comment"]);
    }

    if (empty($_POST["gender"])) {
      $genderErr = "性别是必需的";
    } else {
      $gender = test_input($_POST["gender"]);
    }
  }

  function test_input($data)
  {
    $data = trim($data);
    $data = stripslashes($data);
    $data = htmlspecialchars($data);
    return $data;
  }
  ?>

  <h2>PHP 表单验证实例</h2>
  <p><span class="error">* 必需字段。</span></p>
  <form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>">
    名字: <input type="text" name="name" value="<?php echo $name; ?>">
    <span class="error">* <?php echo $nameErr; ?></span>
    <br><br>
    E-mail: <input type="text" name="email" value="<?php echo $email; ?>">
    <span class="error">* <?php echo $emailErr; ?></span>
    <br><br>
    网址: <input type="text" name="website" value="<?php echo $website; ?>">
    <span class="error"><?php echo $websiteErr; ?></span>
    <br><br>
    备注: <textarea name="comment" rows="5" cols="40"><?php echo $comment; ?></textarea>
    <br><br>
    性别:
    <input type="radio" name="gender" <?php if (isset($gender) && $gender == "female") echo "checked"; ?> value="female">女
    <input type="radio" name="gender" <?php if (isset($gender) && $gender == "male") echo "checked"; ?> value="male">男
    <span class="error">* <?php echo $genderErr; ?></span>
    <br><br>
    <input type="submit" name="submit" value="Submit">
  </form>

  <?php
  echo "<h2>您输入的内容是:</h2>";
  echo $name;
  echo "<br>";
  echo $email;
  echo "<br>";
  echo $website;
  echo "<br>";
  echo $comment;
  echo "<br>";
  echo $gender;
  ?>

</body>

</html>